I have a saniflo toilet saniplus about 4 years old. When we flush the toilet and the tank starts to fill, it fills
Really slowly then it starts like knocking it sounds like its coming from the wall i.e. pipe but when I shut the water valve off the knocking stops .What is going wrong ?

Loose washer, either in the fill valve or in the stop valve underneath the toilet tank. If it sounds like it is coming from the wall it is probably the washer in the stop valve. Replace stop valve.

Thanks I will try the stop valve ,will let you know how that goes.

Toodie...

Just to make sure here, is this a "knocking" or a RATTLING sound?

If you have a knocking sound then proceed as Hkstroud suggested.

If you have a rattling sound then a part (or broken part) has dropped into the GRILLE of the macerator unit and it will need to be cleared to fix the issue, OK?

Mark

Replaced the toilet fill valve today it must have been blocked,was filling slow now it's all good.No more knocking.The water here is full of iron and it must have blocked up the fill valve.