Very slow sink drain (1 Viewer)

[Attila the Hen]

We have an Autocruise Tempo and suffer from a very slow drain on the main sink. It can take up to 5 minutes to empty just half a sink of water. I have done all the usual checks, blockages, tight bends, traps in pipes but can't seem to find anything. One clue has been when the waste tank is 3/4 full, water can come up through the shower plug holes.
I have had a look at the under slung tank and notice that, unlike the fresh water tank, there appears to be no vent pipe in the top of the waste tank. I understand this is common but has anyone out there fitted a vent pipe and, if so, has it improved the drainage from the sink. I was thinking of fitting a 1" vent with a float shut off to stop the tank leaking when full.
Any help or advice would be appreciated.

 

[icantremember]

Does it drain any quicker if you leave the tank drain-off open?

 

[hilldweller]

I was thinking of fitting a 1" vent with a float shut off to stop the tank leaking when full.

Better let it leak, you don't want it coming back through the shower. It's only soapy water after all.

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[Attila the Hen]

I will try it with the tank drain open and see if there is an improvement, a job for the morning.

 

[icantremember]

I will try it with the tank drain open and see if there is an improvement, a job for the morning.

If still slow, make sure all the waste plumbing goes down hill.

 

[kelv]

Just a thought have you checked your van is level even a slight slope can slow the water going down .
On my van I had to alter the fall off one pipe as it had a slight back flow even when the van was level.

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[TerryL]

This might sound daft but...........

I can usually "assist" the slow drain by swirling the water around the plughole with my fingers to create a whirlpool. I think the science behind this is that you somehow allow a bit of air to mix in (or out, I dunno).

I think the real reason for it being slow is, as suggested above, there is insufficient fall on the waste pipes - got a similar problem on a sink at home where I cannot get a good "fall" on the waste.

 

[Techno]

A kettle full of boiling water

 

[tofo]

We have an Autocruise Tempo and suffer from a very slow drain on the main sink. It can take up to 5 minutes to empty just half a sink of water. I have done all the usual checks, blockages, tight bends, traps in pipes but can't seem to find anything. One clue has been when the waste tank is 3/4 full, water can come up through the shower plug holes.
I have had a look at the under slung tank and notice that, unlike the fresh water tank, there appears to be no vent pipe in the top of the waste tank. I understand this is common but has anyone out there fitted a vent pipe and, if so, has it improved the drainage from the sink. I was thinking of fitting a 1" vent with a float shut off to stop the tank leaking when full.
Any help or advice would be appreciated.

Have you checked inside the pipes for solidified fat

If you weren't the first owner a small blockage attracts more stuff

You may be more carefull than the first owner

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[Attila the Hen]

Thanks for all your help, looks like the solution is a tank vent. Tried the sink half full of water with the tank drain open and the sink emptied much faster. Will need to slim down a bit so I can get under the MH and work on the tank - no perhaps I will put it up on ramps.



Failure is not an option, in my case it is more of a feature.

 

[mikebeaches]

If still slow, make sure all the waste plumbing goes down hill.

Noticed our brand new van had a very slow draining kitchen sink. Looked underneath and noticed the waste pipe went up hill!! Tried to move it without success. Took it to the dealer and he cut an inch off the down pipe - works a treat now.

 

[iandsm]

I

Thanks for all your help, looks like the solution is a tank vent. Tried the sink half full of water with the tank drain open and the sink emptied much faster. Will need to slim down a bit so I can get under the MH and work on the tank - no perhaps I will put it up on ramps.



Failure is not an option, in my case it is more of a feature.

I had exactly the same symptoms which as in your case improved when the drain valve was opened. It seemed to me that the air in the tank could not escape fast enough so I got underneath and inserted a length of curtain wire into the breather/ overflow oipe them inserted a garden hose and turning it on forced a backflip. This removed what must have been a build up of debris/fat and the problem is now solved. I will now ensure we don't allow the tank to fill completely thus avoiding water with fat floating in top to block the vent. I expect if you fit a vent/ overflow your problem will be solved as mine was.

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[Rollmop33]

A vent and slight mods to the pipe runs has helped a little but it looks like we may have to put up with a slow drain. I think the main problem is the pipe runs as some are uphill but chassis members get in the way of making all pipes have a fall to the tank.
Thanks for all your help and suggestions

 

[pappajohn]

One clue has been when the waste tank is 3/4 full, water can come up through the shower plug holes.

How do you know its 3/4 full ?
Using the gauge ?

If so ignore it....gauges are rarely accurate.
Waste coming back up through the shower plughole indicates the tank is over full.

 

[Jaws]

The main sink in our Autotrail was a VERY slow emptier
Looked at the trap underneath and it was stupidly small.
Replaced it with a decent sized one ( actually bought from @Gromett a couple of years ago ) and after fitting it cured the problem completely

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