you can buy or build an overflow. the type above cost about 6$ to build.
they are very easy to build, you do not need to drill glass as they hang on back. And they create a continuos siphon, that does not loose suction even when water drops below overflow(ie. water changes, power outtages). when the water goes back above the over flow it starts working again,on its own.
also by putting 2, 1 on each side of the you will diffenatly lower chances of somting going wrong.I doubt 2 would ever fail at the same time. like I said, I
have been using these for about 5 years,an never had 1 stop working,unless I stopped it, by blowing air tru it.
also I think youtube has vids of these, search pvc overflow.
IMO, I think tanks with built in overflows are a huge waste of tank volume!
also rubbermaid or sterlite wet drys, or sumps can be done under 20-25$. I use these on all my FW, FO,and FOWLR. the serilite 3 drawers storage containers hold large amounts of fiter media, about 5 gallons each drawer.
IMO. for freshwater,or fish only they blow any store bought out of the water.
And to be able to slide out a drawer to change out media, is easy and awsome! this setup can also be changed around to make a refugium.
you should only spend your money on a good return pump!
The rest DIY all the way!!!!!!!!!!!!!!!!