fresh Water tank leak

The Herald, bless it, is  a V reg, 

Very powerful with a 2.5 TD engine.

I will look at the seal on the cap and the top of the tank, and I guess a new washer first.

Thanks for help so far.

Tonker

I have an onboard water tank in my motorhome. If I over fill the tank, say 100% plus, I do get some water leaking. If I fill to 95% no problem at all which I find perplexing. Its not coming out of the tank top seal as I always have a towel over it and it never gets wet! Is there evidence of water coming out of the top of the tank, i.e. wet around the seal? Short of removing the tank and sort of bench testing it I have not been able to find an answer so am now very cautious about over filling. 

David

David, in my experience fresh water tanks 'overflow' in one of two ways....

either, as both my swifts did, the tank has holes in the very top and water just runs out all over the place under the van, first thing you know about it is wet feet!

or, as in our two Carthagos, the waste has a small breather in the top of the tank which runs right back up along side the input filler pipe and vents out into the filler hole in the side of the van, effectively overflowing back from the water entry point...simple system and it's obvious when the tank is full.

when filling, I stick the hose in tank, step inside the van, watch the water guage rise until it hits full then walk round to the filler and gradually reduce the speed of input until the water gently trickles out the filler hole...tank fully brimmed, no mess.