Close coupled seals

[notaclue]

Fitting a new closed coupled WC & the cistern to pan seal is a crappy foam ring, there is no way to see if it is locating properly when fitting the cistern down
Any suggestions...................?

Thanks

 

[Plumbstar Tom]

good old donut washer, never had it fail to be honest not much effort to swap it if it did but new ones are normally fine