Leaking cistern on close coupled wc

[tonyb61]

We've installed a new close coupled wc in the bathroom. It is the type which have a rubber doughnut washer on the flush valve outlet to seal the flushing water flowing from the cistern flush valve to the pan, and two long plastic bolts which feed through two holes in the cistern bottom through holes in the pan base on to plastic nut below, clamping the cistern and pan together compressing the rubber washer around the flush valve, and using the tops of the bolts pulled tight to seal the 2 holes in the cistern. I'm getting a slight drip through the hole in the cistern bottom down one of the bolts, it just wont seal the hole in the cistern properly.
Is it ok to use something like lsx applied to the underside of the plastic bolt top, and the hole in the cistern to help seal the hole in the cistern bottom better ? Or is there something better ?
Thanks

 

[joni os]

Buy a repair kit with stainless steel bolts and rubber cone internal washers to seal cistern holes. Even with these I silicone the cones first. Ensure nut tightened against cistern to compress cone washers before fixing to pan, and when fixing to pan do not allow bolts to rotate as this will loosen nuts.

 

[Best]

^^ same as above. I immediately thought on the bolts supplied are probably just with flat rubber washers. This can mean the bolt risks not centering and tightens to one side of the hole and the washer won't seal. The tapered washers and stainless steel bolts do a great job.

 

[tonyb61]

Thanks for the tips, I've searched on google for those, they are quite common....
It's pretty crap that a brand new wc needs a additional kit to work properly though, it wasn't that cheap !

Thanks
Tony

 

[Phil]

Even with the proper bolt set with coned washers they can sometimes leak by water running down the thread, water gets under the head of the bolt from the metal to metal contact of bolthead and washer, use clearfix/plumbers gold on mating surfaces.

I figured this out a few years ago when I just could not get it watertight, whatever I did it dripped I must have had that cistern off 7 times, one more and I would have kicked it in.

 

[plumben]

I always use clear silicone on the bolts, silicone round the top of the bolt head, oust the rubber washer into that, wipe excess off silicone rubber push through holes bolt up

 

[Best]

Problem with the bolts supplied with many toilets and other things in plumbing is they have been designed by people who are not plumbers and haven't a clue how to seal anything.
A penny pinching idea to supply on some cisterns steel bolts that will rust is also ridiculous.
Another idea that comes on Chinese toilets is big plastic bolts to hold pan & cistern together. While that is hopefully okay and won't rust, they often come only with one nut and therefore if the domed washer compresses a bit, then the bolts are no longer tight to the cistern.