Mobile Home Toilet Still Runs with New Flapper Installed

I have a mobile home toilet that still runs even after installing a new flapper. If I press down on the new flapper the water quits running into the bowl. I've cleaned the edge where the flapper rests. How can I fix this. Is there some kind of replacement part?

You might supply a bit more information. Make and model of toilet and make and model of the flapper would be a good start.

Thanks Gary. Can I find this information underneath the tank lid?

Not all generic flapper valves will fit all toilets. But, the first thing to check is that there is enough slack in the chain, and that there isn't too much and it is caught underneath. On some, they have hooks and a round sleeve for those that don't have hooks. If you have hooks and you used the sleeve, you need to cut out the sleeve and only use the hooks.