well 'Shower Plug' has a 10 year warranty so If you paint that on at leased every 10-15 years(!) on the tiles and grout- you will never have a problem. Can't find the coverage though (bunnings website has it wrong)- you'll have to find out - there's also 1L tins.
Theres digger's Sealant Showercoat. cheaper, no warranty specified. 500ml will cover approximately 16m2
http://www.bunnings.com.au/sealant-show ... r_p6651334
the Tile Guard above seems fine- but I think maybe no warranty. there are ones just for the grout. there are quite a few products- I just searched the bunnings website for 'shower sealer' 'tile grout sealer' etc. I would find the coverage of 'Shower Plug', to see if it economical- though, it will last over 10 years. otherwise try to find one with a warranty or reputable brand or other h/ware stores.
but try to get 'Shower Plug'