Are you on a municipal sanitary sewer system? Or perhaps a backyard septic field?
Speaking from the perspective of a person who has at various times been on both of those types of sewer systems, and who now relies on an ejector system on my own property, I would suggest that you carefully consider all aspects of where your water is going before making a lot of labour-intensive mods to your current set-up. If your system is entirely on your own private property, i.e. a septic field or ejector, then you are placing unnecessary and undesirable strain on your ejector/sewage pump and/or septic field by pumping many hundreds of gallons of excess water into and through them. Both of those components have a finite working life; once that is used up, repairs (especially in the case of the septic field) are extremely expensive.
Unless there is some pressing reason to avoid doing so, my first choice would be to plumb the outflow directly to the outdoors and by-pass your waste-water system altogether. My current set-up drains through a line running through my wall and into a buried pipe that runs down-grade away from the house, under my lawn, and ejects the water into an adjacent field (my own property). In my case, a pump is required to move the water up out of my basement fishroom and out through the wall; if your fish tanks are above grade, this could be done using gravity instead. This would work especially well in your area since it could function this way all year round; in my case there are at least 5 months of the year when the outside drain must be switched to an above-ground flexible hose which I need to be able to access to break up ice and keep it from clogging.
Do you have a basement with a sump pit? If so, you could very easily drain your waste tank water into that, and simply rely upon your sump pump to automatically eject it to wherever it is set up to transport the ground water it catches now. This requires keeping a regular watch on your sump pump to make sure it is functioning properly; this is something that should be anyways. Again, the sump pump has a finite life, but in this case having it run intermittently all year round, rather than just during wet times, may actually increase the service life of the pump. And, of course, compared to sewage pumps and/or septic fields, sump pumps are cheap.
Thinking through all aspects of this part of your tank maintenance system will pay big dividends in the long run. The easier it is to change water, the more likely you are to do it regularly. And the basic truth is that all the filters and other water-quality devices with which the modern aquarist loves to fiddle are simply devices that prolong the length of time between water changes and allow us to cram higher densities of fish into our tanks. Enough water changes, especially when combined with moderate stocking densities, make any filtration unnecessary.
Think twice (or thrice...or even more often...) and then start cutting, drilling, gluing, etc.
