With as little break between events as possible:
This will be easier for some and harder for others, depending on where you live, where your pool is, etc. If possible, plan this so you can finish your run at or near your pool, and then begin your ruck from there. For most this will mean going to your pool, and leaving your ruck in your car, running in the area around the pool building, coming in, swimming, then going back out to the car and getting that ruck. The faster you transition (i.e. get changed, get from pool to ruck and so on) the better your time will be. This should be treated as practice for a triathlon.