thefford weak flush

[Fatboy]

hi all,
just been to my daughters ans she has a vert weak flush in her thetford cassette toilet, its a compass vintage 1994 so as you would expect its a manual flush, the water is filled to the top but as you turn the handle it feels very weak in how much water it sends around the lid, i pressumne it works of some kind of vaccum ? can any body expliain how it works and has anybody ever come across this before.......thanks

 

[Sproket]

Have a look here Repair instructions for all Thetford Sanitation products
It's a downloadable pdf file ......( you will have to save & open it )

It's possible the plastic bellows have split ......

 

[forestgump]

take the plunger out at the bottom is 3 claws that grab the belows norm one of these claws is broke replace the lot and the new one comes with the sealent .