Unblocking My Wash Basin Drain

Unblocking A Bathroom Wash Basin Drain


I recently noticed the waste water leaving my bathroom wash basin was taking more time than usual to drain away. Realising this meant a total blockage may be imminent, I set to work dismantling the waste pipe and bottle trap so that I could begin unblocking my wash basin drain. Boy was there some gunge to clear out.

This operation can involve spilling DIRTY water and using BLEACH. So be warned and be prepared. — HC

Select pictures to enlarge them and get a better view.

Tools Required


  • Use eye protection when spraying bleach.
  • Use rubber gloves when handling bleach or bacteria laden gunge in waste pipes.
  • Wear old clothes in case bleach is spilled on them.
  • Get help to lift heavy objects.

Gaining Access To The Wash Basin Drain Pipes

My wash basin is an Armitage Shanks Ascania semi-pedestal variety. That means the basin is bolted to the wall and is not supported by a pedestal underneath it. The pipes are then covered with a ceramic cover known as a ‘Semi-pedestal’ which has brackets fixing it to the wall. It looks a bit like the top half of a pedestal but it does not provide any support for the basin. I installed it in 2005 so I am familiar with the way it is fixed. Hopefully my description here will help anyone who has never dealt with one before.

How My Semi-pedestal Is Attached To The Wall

Unblocking My Wash Basin Drain
The Semi-pedestal Fixings

Above: The semi-pedestal is fixed by two continuously threaded screws. These pass through the top corners of it and screw into plastic right-angled brackets which are firmly bolted to the wall through the bathroom tiles. The brackets have many holes in them which are all close together. When the semi-pedestal is presented to the underside of the wash basin the fixing screws are screwed into whichever holes are most convenient.

The fixing screws are sleeved and cushioned with plastic ferules to prevent damage to the porcelain. The ferules have a countersunk head on the outside which fits into holes in the porcelain of the semi-pedestal. When the screws are tightened they sit nicely in the ferule heads and clamp the porcelain to the thick plastic brackets. The screws are finally covered with a good quality screw cap.

If the right-angled brackets are positioned correctly the semi-pedestal won’t drop down under its own weight when the screws are tightened. The plastic brackets are nearly 1cm thick and suitably strong and held to the wall with anchor bolts and washers. They have to be positioned to sit flat against the inside surface of the semi-pedestal so that there is no flexibility when they are clamped to the semi-pedestal.

Removing The Semi-pedestal

I had to take the semi-pedestal off the wall by first removing the screw caps which had to be flicked off with a thin bladed knife forced under the edge.

Unblocking My Wash Basin Drain
Supporting the Semi-pedestal

Before removing the two screws the semi-pedestal required support from underneath. A strong person could hold it up but to keep holding it with one hand, while removing what might have been difficult to remove screws with the other, would sap the strength of the best worker. I used a plastic children’s step atop a plastic kitchen step as a support. They didn’t quite fit under the bottom edge of the semi-pedestal, but since it has a sloping bottom surface I was able to wedge them under it by pushing the top step towards the wall.  Each screw could be removed half way and still support the semi-pedestal but for final screw removal a good support was required, so I kept holding the support in place with one hand while unscrewing with the other. Another pair of hands would have helped.

Good Advice

The semi-pedestal is heavy. If you think you can hold it with one hand while unscrewing with the other without extra support, then consider this:

  • A situation where you are removing the last screw and the screwdriver slips out of your hand and rolls out of reach. How will you retrieve your screwdriver without letting go of the semi-pedestal and possibly damaging it or the bracket when it dangles precariously?

Unblocking My Wash Basin Drain

With the semi-pedestal out-of-the-way the underside of the wash basin looked like this:

Unblocking My Wash Basin Drain
The Wash Basin Hot & Cold Water Pipe and Waste Pipe systems

Removing The Bottle Trap And Waste Pipe

Unblocking My Wash Basin Drain
Preparing to remove the Bottle Trap Bowl

Before dismantling any pipes I put some old newspaper on the floor and placed a bucket under the bottle trap to catch the water from it. If the floor had not been waterproof I would have put some polyethylene sheet down first.

The bottom of a bottle trap has a screw on bowl (cover) which can be removed for cleaning or removing small items lost down the plug hole (waste) of a basin, e.g. jewelry stones.

I then unscrewed the bowl on the bottom of the trap with the aid of a “Boa Constrictor” wrench. I had to grip the trap firmly, to apply a reactive force, while unscrewing the bowl .

What Is A Boa Constrictor Wrench?

Unblocking My Wash Basin Drain
Boa Constrictor Wrenches

A Boa Constrictor wrench is type of strap wrench. It’s a plastic wrench with a rubber strap which wraps around the item to be turned. The handle is then used as a lever to turn it. The Boa Constrictor wrench has to be applied such that it grips tighter as the force is increased. One of these is almost as good as a Stillson wrench and more suited to working on plastic.

I’ve had a pair of Boa Constrictor wrenches, shown here, for a long time and have since acquired a second pair. I found it necessary to use two of the same size when, for example, opening a jar with a tight lid. One is wrapped around the jar to give a clockwise movement and the other around the edge of the lid to give an anticlockwise movement.

Examining The Bottle Trap

Gunge seen looking up into the Bottle Trap
Gunge seen looking up into the Bottle Trap

When the bottle trap bowl was removed the dirty water in the trap poured into the bucket. I then looked up into the trap with my camera to see this.

As I expected it was very dirty so I then removed the whole bottle trap and pipework and took it outside in the bucket for cleaning.

Gunge hanging from the Waste Pipe after removing the Bottle Trap
Gunge hanging from the Waste Pipe after removing the Bottle Trap

To remove the Bottle Trap I unscrewed the top nut from the Waste Outlet where the waste water goes into the trap. These nuts should not be excessively tight. They do have a soft rubber sealing washer and the water pressure is low. I didn’t need to use a Boa Constrictor wrench.

Once unscrewed I lowered my trap from the Waste Outlet. It was flexible because the waste pipe plugged onto a right-angled bend (elbow) which could twist around on the original copper waste pipe to which it fits. The trap could then be removed from the Waste Pipe by unscrewing the other nut where the waste water goes out of the trap and into the waste pipe.

Examining The Waste Pipe

When the trap was removed I could see how much gunge was in the waste pipe.

I then pulled the short waste pipe out of the elbow and put that in the bucket. The gunge was hanging out of the elbow too. So I removed that by twisting it off the horizontal copper pipe under the tiles by working it up and down and forcing it to the right at the same time. That too went in the bucket.

At that moment water and gunge came out of the horizontal copper pipe so I had to make a quick move with paper towels to stuff them underneath the end of the copper pipe to soak it all up.

Gunge in the old copper to plastic pipe adapter.
Gunge in the old copper to plastic pipe adapter.

Using Strong Bleach To Clear Gunge From The Wash Basin Drain

I then took a bottle of HG Mould Spray (a chlorine-based bleach) and squirted it directly into the copper pipe after repacking the space below with dry kitchen roll sheets. I squirted plenty into it in the hope that it would react with the gunge in the pipe and dissolve as much as possible. This pipe, in my case, is only 600mm long before it goes into the vertical stack pipe. If I had found it seriously blocked I would have cleaned it with a long pipe brush I have.

I took all the components I had removed in the bucket to an outside tap and washed them thoroughly with bleach and an old toothbrush before returning them to the bathroom for reassembly.

With the bucket placed under the open waste outlet I squirted HG Mould Spray into the waste outlet from above. There are two oval holes a little way down from the top of the metal waste outlet. The overflow water that enters the basin overflow exits from the inside of the basin at this point through these oval holes and passes into the trap. I did my best to work the mould spray in with the toothbrush. After leaving the bleach to work for 15 minutes I ran warm water from the tap and used it to rinse the area I had bleached.

Reassembling All The Dismantled Parts

Reassembly is very much the reverse of the dismantling procedure. The push fit pipe joints went together easily. If they hadn’t I would have used some petroleum jelly to lubricate them. Some people use washing-up liquid. Below is an image of the plastic pipe parts laid out clean and ready to be assembled:

The plastic parts of the Waste Pipework.
The plastic parts of the Waste Pipework.

The Reassembly Procedure Is:

  1. Put the right-angled elbow on the old copper pipe.
  2. Plug the short white waste pipe into the elbow.
  3. Screw the bowl onto the bottom of the bottle trap and tighten.
  4. Put the nut, plastic washer and rubber cone onto the end of the waste pipe.
  5. Present the bottle trap to the waste pipe and screw the nut onto it taking care that the rubber cone seats well in the process but don’t tighten yet.
  6. Screw the captive nut at the top of the trap onto the bottom of the waste outlet.
  7. Tighten both nuts on the trap gradually moving back and forth between the two so that both joints seat correctly.

Testing My Wash Basin Drain Pipes For Water Flow & Leaks

When all the pipework was reassembled I ran water into the wash basin and tested for leaks from my wash basin drain. There were none. However I noticed that water still built up in the basin so there might still be a partial blockage in the wash basin drain. There may still have been gunge in the old copper pipe which I had difficulty cleaning. I tried to shift it with some boiling water by pouring three kettles of boiling water down the drain. That improved the water flow. The gunge is made mainly of soap fat which melts in boiling water. Several kettles of boiling water were needed in quick succession because a lot of heat is given up to the pipework. It all needs to be raised to a high temperature to melt the soap fat.

NOTE: I think you can reduce the gunge created in waste pipes by using liquid soap instead of soap bars.

Refitting the Semi-pedestal

Again this is much the reverse of the procedure to remove it. After cleaning it with a vacuum cleaner and a damp cloth I lifted it into place and wedged the plastic steps back under it to support it. At first I had difficulty locating suitable holes in the brackets. So I removed it and trued up one of the brackets and tightened its anchor bolt. I lifted the semi-pedestal back in place and supported it as before. This time I managed to find holes as desired (hopefully the original holes used initially) and tightened the screws. Then I clicked the screw caps into place. “Job’s a good one.” (A colloquial expression used by tradesmen when they complete a job successfully.)

Further Reading

See my post Unblocking a Blocked Toilet



2 responses to “Unblocking A Bathroom Wash Basin Drain”

  1. Lizzy Booth avatar
    Lizzy Booth

    Thanks for your detailed description of how to do this. It was extremely helpful in clearing our sink. I especially liked the well labelled photos. It would have been inconvenient to wait days for a plumber and I don’t think I would have felt I could undertake the task without seeing this post! Thanks.

    1. Helpful Colin avatar

      Hi Lizzy,
      Glad to be helpful.
      Regards, Colin.

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