To much of a good thing. Help.

So I am 3 weeks into flowering on my first grow. All is really well except that my plants have out grown my system. I am using a DWC with three inch net cups in a 2'x3'x6" tub and plants are to tall and heavy, causing them to tip and then push the netcup through the top of the container.(myroom is 3'x4'x7') I have strung up some yarn running across the room to support the plants, but I am now left with the problem of how to clean my tub once a week.

So my questions are:
Can I just siphon new water in for the rest of the flower cycle and not clean the tub?
If not, What would be a better way to support the plants?

A little more info on the grow.
4- purple trainwrecks
1- blue cheese
1- connisuer
I do know that on my next grow that I will avoid growing 3-4 foot plants in 3" netcups.
Hopefully this isnt the catalyst for my ggrow going to shit.

Whats Fonzi?

could you not put some bolted eyed hooks through the lid an tie them to the roof use some washers though should work

i have the same problem, well i dont really consider it a problem, my plant has gotten so big that it has leaned pretty hardcore over the side, but it is also cuz i LST'd it because they were getting too big, its not a problem to clean, i just take it out put em in containers that can hold the net cups and add water, then i take my rez and wash it out. takes like 30min to do it all, you could tie em up all u want, they will only get bigger. you can check mine out in my signature, only one is doing it tho. i perfer them to lean a bit so light gets to all the bud sites.