Flomasta bottom entry fill valve with 5mm thick Poly Cistern

[GeoffG]

Flomasta fill valve bottom entry with brass shank, v 1.1

Looks great but the instructions say the cistern thickness at the bottom mounting point must be min 8.5mm. Just a diagram - doesn't say why.

My cistern is a concealed one made of polythene or something like it, and is only 5mm thick.

Will be it be OK, do you think? What's the reason it says this and what is the nature of the risk if I fit it anyway? Might it leak? Seems unlikely.

Can anyone advise?

 

[steadyon]

It has a downwards facing conical washer to make a watertight seal inside the cistern. With a "thin" cistern base, this might not allow the washer to wedge in correctly.