They, the 701 toilets, are also of a new design for the SW network. Previously any train of recent times, 458, 444, 450 etc, has to visit a CET (Controlled Emission Toilet) discharge point to have their tank contents emptied and dealt with at least once every 48 hours in the plan, which is one reason unit diagramming in todays world has become more complicated than it was when toilet waste was simply dumped on the track every flush (VEP's, CIG's etc etc).
There are only a handful of CET discharge points on the network, and these are largely within depots. Bare in mind many unit diagrams do not see a depot for two/three days, as per above.
The benefit of the new chemical toilets on the 701's, is that the waste can be dealt with to a large degree in the tanks under the unit, and so visits to depot for CET discharge will in theory be far fewer. I had heard once every three to four weeks would be sufficient, but what the situation is today, now the units are up and running, I do not know?
But in essence, the idea was/is that units could stay in service for far longer between depot visits, thus freeing up more depot time for other maintenance initiatives etc.
Things may well have moved on, so apologies if I am now out of date....