Slow drainage from sink - public house

[jim127]

Hi,
Can't find anything specific related to this problem in previous posts but there are a lot to search so apologies - it is a bit of a long post!!

Local pub has a problem with their glasswasher - it doesn't empty properly. First thought is that the drainage hose needs repositioning (it looks very tangled) and plumbing into the drainageIn actual fact when I had a look the sink it drains into also drains very slowly. Cleaned the trap - still slow drainage from sink. It is an S type trap, 40mm that goes down into the cellar.
The glasswasher and the pump/beer line cleaner both join the sink drainage pipe below the trap.
Had a look in the cellar-
Another sink (unused) and coffee machine drain, via S traps into the comon drain - this is a bit up and down but meets an old metal drain (via another trap - small U bend) which then disappears into the cellar wall to go who knows where - it is a very old building.
Undoing the trap the water seems to flow more freely.
So a few questions I would welcome your thoughts on:
- could the presence of this extra trap be causing the problem if for example it is interfereing with any ventilation?
- obviously the slightly up and down nature of the pipes in the cellar aren;t helping but I am not sure with the position of the metal pipe that this is easily fixable. Is it just a case of optimising this if removing the trap doesn't work?
- I guess there could be a blockage in the metal pipe but I don't suspect this as there was no backflow of water from that direction when I undid the trap - is that flawed logic?
- I am planning to fit a new trap on the sink with a spigot for the beer line - which is pumped and seems to drain ok - and another possibly HepV0 type valve and spigot for the dishwasher so this can be connected below the floor in the cellar. All with the warning to the landlord (a mate) that this might not help the drainage!! Any thoughts on this plan?

 

[Simon F]

without a continual fall the waste will always be slow to empty and prone to becoming blocked.
if the pipe length is over 3m for 1 1/2" then it needs venting to avoid issues with negative pressure.
lots of things and pipes all combining will also create problems.
sounds like the whole lot needs redoing properly.

 

[jim127]

Thanks for that Simon. I think that would mean a new drain to get the fall so huge amount of work. I am hoping removing the second trap (the one in the cellar) might help if there is a vent pipe further down the drain.
If it doesn't then they'll need a drain expert and large pockets I guess.

 

[REDSAW]

miss the days working in these places 30 years ago.lol.
try putting in an aav at the highest part and sink filters in below as there is all sorts shoved down by the staff especially over weekends.
that should work or the waste needs upgrading in places to 50mm if not already so.

 

[jim127]

Thanks Redsaw. Not sure I can fit an AAV - doesn't that need to finish above the spillover level?
Or could I fit one in the cellar? Sorry if I am being slow.
Could I upgrade to 50mm even though it is then going back to smaller pipe downstream? ie. the old metal pipe is only 40mm I think. It is a very old pub that had a refurbishment upstairs a few years back - moved the bar and hence these long runs of sink drains to the old existing drains.

 

[Simon F]

if you increase the pipe size you don't want to then go smaller
before when you mentioned the metal pipe I imagined you were talking about the stack pipe
but you say its 40mm waste, presuming copper?
can you not remove it and redo all in new plastic waste 40/50mm depending on length of run
giving the pipe a continual fall to the drain

 

[stevetheplumber]

two traps on one line will often stop altogether id remove one
for some strange reason pubs seem to be exempt from any form of building controll 60 foot of 32mm pipe hanging on string the length of the cellar draining 4 sinks seven urinalls 4 basins and two glass washers is the norm, provided it runs uphill at at least two places and doesnt contain any rodding eyes

 

[REDSAW]

two traps on one line will often stop altogether id remove one
for some strange reason pubs seem to be exempt from any form of building controll 60 foot of 32mm pipe hanging on string the length of the cellar draining 4 sinks seven urinalls 4 basins and two glass washers is the norm, provided it runs uphill at at least two places and doesnt contain any rodding eyes

thats the one.lol.
you forgot terminating internally into the kitchen grate!.

 

[jim127]

Steve - you have described it exactly - down to the string :rockon2:
Simon, the small bore metal pipe dissappears into the wall - in my first visit I couldn't find where the drain/stack that this drains to is as it disappears into a wall which runs further into the pub rather than to the outside - it is quite a large pub, as I said previously very old - marketed as the oldest pub/building in town - and the nearest outside wall is directly onto the high street - no stack there and none I can see coming though the roof.
I'll remove one of the traps and see if that helps together with replumbing the glasswasher. Hopefully it can't make matters worse. And if not I'll see if I can do anything to produce some falling gradient to the offending metal pipe.
Thanks all for your help - I'll let you know how it goes.
PS - redsaw - there is a sluice/open drain of sorts in another part of the cellar - I am tempted to move things in that direction but because of the chemicals they are always pumping into the system..........