hello
You can still sometimes get smells back up through the waste grate on your bath ect even when traps are full of water this can be caused by a sort vacuum in the drainage pipes when you empty bath/basin of water you could try adding anti-syphon traps to basin/bath/shower which will stop such vacuums happening.

Also those whirlpool baths can get mold in the pipework and pump which can cause smells these can be cleaned out be adding baby bottle sterilizer to bath and running that for a while.

hope this is some help to you.

www.heat-pack.co.uk

Sometimes there are these type of smells if the pipes haven't been used for awhile, Was the house vacant for an amount of time before you moved in? If this is the case the more regularly you use your water then the smell will get washed away. Otherwise you may have a problem with blocked drains. If this is the case you will probably find out next time you have a party or the like with excess use of the toilets causing them to overflow. If this happens you need a plumber to come out and unblock the drains using an Electric Eel or/and High Water Pressure Jet. If this finds a blockage that that they can't clear then you may have replace/repair your pipes. If so look at the alternative which is to Reline your pipes. This way you can save you thousands of dollars.