Thinking of capping off hot tub drain pipe to reduce risk of biofilm or other growth in that pipe? Thoughts?

[DougA]

I have a 400 G. hot tub.  I'm thinking about covering my drain at the bottom of my hot tub with Flex Seal Paste the next time I drain it to reduce the risk of biofilm and other stuff growing in that pipe that flows out of the tub to drain it.  I'm curious if my Ahh Some flushes clean that pipe sufficiently because the water in that pipe is just standing water versus the moving water in the jet lines and tub.  I don't really need the drain because I use a sump pump to take drain the water and a shop vac to get the remaining water.  

Do you think sealing the drain would be helpful for reducing growth or is this likely unnecessary?  

Do you think "Flex Seal Paste" would be safe in the tub.  They claim it is?

Thanks!  Doug