visit the plumbing dept & get some bulkhead compression (or push-in) connectors.
dead easy - just put a connector at the bottom of each bucket & join them up.
Don't forget to add a drain tap
do not scrimp on airstones & pumps. The bigger the airstones & pump, the frothier the water & the bigger / healthier the plant will be.
It's worth buying 2 pumps & connecting them both up so u still have air if 1 pump fails.
If u lose a pump, ur plants will die within 48hrs, so at least have a spare 1 to hand.
Cheap pumps & small airstones are false economy.
Just a point about joining the tubs together......... I know it makes ph'ing etc a lot easier, but u will find that some plants need a lower strength feed than others.
Some plants' roots will develop faster than others & u will be stuck with the same level in all your buckets.
It's really not hard or overly time consuming to maintain 6 buckets individually.
Mix & ph your feeds beforehand - undiluted. Then add to the fresh water to get the ec u want for each separate tank.
If u are joining the tubs together & adding the undiluted feed to 1 bucket, i can more or less guarantee u will kill that plant as it will take a while for the feed to circulate & mix properly with the water in the other buckets.