Hi Hank, to be honest I can't see it going anything other than stopping water from draining out, I assume you will be using large pots, so it's going to take a while for the roots to get down to the comfrey anyway, by which time it may have started to decompose and release some nutrition, but I would just use normal tom fertilizer, and make liquid fertilizer out of the comfrey, Derek.

Ive used comfrey for many years now and i swear by it, but ive not honestly heard of putting it in the bottom of a pot,
But having said this your friend may well have hit on something here,
So why not try it on one pot and let the rest of us know if you've strangled your friend after the end of the tomato season?

Ref comfrey its excellent on the compost heap and it you've a 45 gal drum (cleaned out of all oil etc)
I cleaned mine by burning twigs in it and then 3/4 filled it with water and put two half sacks (large onion nett bags will do) filled with comfrey leaves, & a brick to help sink the bags,
Leave thes until you start to get a smell "& it will really pong so think where your going to have this drum as the neighbours dont need to smell your hobby.
After a month approx the mix would have settled down and its now you have one of the best liquid home made fertilizers you can have, the mix with cold water is 9 parts water and 1 part the comfrey mix.

Give it a try and save yourself a small fortune on bought liquid mix.

Thanks to both of you guys, I will try it in one pot just as an experiment. Although my toms did really well last year.

Yes agree with dungy, damn good stuff ive been using it for years, by the way dungy have you tried this method with nettles ?