Strange behaviour of macerator toilet

[dal5band]

My son bought this house with a Sanitop/BroyPro macerator toilet the previous owner had installed as a downstairs WC. The toilet appears to work ok to start with then there is water coming up the adjacent wash basin. On the flushing, the cistern empties and the macerator pump runs normally. The cistern fills with water and then there is a wooshing sound and water squirts up the sink waste pipe into the sink. We keep a plug in the sink to keep it from squirting up from the sink plug hole.
The waste pipe has quite a long horizontal run into the stack at the back of the house.
Any ideas what causes this pressure wave ?

 

[flameport]

Incorrectly installed, basin waste is connected to the same waste pipe as the macerator.
Correct option is to have both the basin and toilet connected to the macerator, with the outlet from the macerator going directly to the stack.

 

[Hugh Jaleak]

+1, not unheard of for people to connect an adjacent appliance to the (pumped) outlet from the Macerator. There is a tale of one Property with such a setup, who kept a sandbag in the basin to prevent the plug from blowing out under the pressure from the macerator!

Tee where basin joins the macerator outlet run needs cutting out and and replacing with a straight run, (solvent welded pipework is a must!), then connect basin waste to inlet side of macerator.

 

[just pumps]

The fact that there is a long delay before you hear the whooshing and see the water enter the basin leaves me think that the discharge pipe isnt totally clear.

 

[just pumps]

Incorrectly installed, basin waste is connected to the same waste pipe as the macerator.
Correct option is to have both the basin and toilet connected to the macerator, with the outlet from the macerator going directly to the stack.

Whilst I fully onderstand where you are coming from guys the Sanitop doesnt have a low down side connection for the basin waste being a w/c only unit, and the basin can be connected to the outlet pipe but certain restrictions to the installation do apply.

 

[dilalio]

I might be wrong, but...

How does a mechanical device have a "behaviour"?

Sorry. Couldn't help it. Just sayin'!



Edit: "Action" not "behaviour"!

 

[dal5band]

Finally got a photo - looks like there may be a spare port to connect the sink ? The one in the background next to the Flexi ?

Macer

• dal5band
• 21 Jul 2021

Macerator

 

[just pumps]

Yep, slice the top 3mm off it and use a soft rubber connector. TBH I had forgotten about that connection.