How long do you store fresh water in tank?

You need to not confuse the septic smell with fresh water unless you are from a very mineral rich water system (South West) the water tends to be odorless.

Yes Fresh Water may go INTO your 'FRESH water' tank smelling just fine.

Now, USING the fresh water within your coach add dirty soap from washing and showering, toothpaste, spit, grease, food stuffs etc ALL that then goes INTO your "GRAY" water HOLDING tank.

It is NOT odorless when dumped on the ground.

I have been parked next to people who drain their gray on the ground, it STINKS and STINKS bad. Don't care what the laws about it are, it is INCONSIDERATE of other campers to dump your gray tank at your site.