Installing grey water tank

Looking for a bit of advice, we currently have a Smev sink in our van the outlet from this drains via some convoluted waste hose straight through the floor, see picture of outlet, we then place a Fiamma grey water roller tank under this to catch the water that comes out.



As you can imagine this is an absolute pain in the *** most of the time, if the ground isn't level the tank either can't fit under the van or the pipe is too far from the tank, I have lost count of the amount of times I've forgotten about it and tried to drive over it and emptying is a nightmare especially in aires etc. it can look suspiciously like we are emptying our toilet. Recently we have taken to replacing the tank with a collapsible bucket and emptying as we go but again its not ideal.

So I've decided to fit a proper grey water tank and have got a tank that is shaped to fit nicely over the rear wheel arch. See picture with tank and fittings supplied. My big concern now is to actually fit it correctly to avoid smells coming back into the van.
I was going to run the waste hose I currently have to the top of the tank clamping it on the way to form a u bend. I presume the tank needs some form of vent from the top/overflow pipe. Would it be ok to bring this out of the top of the tank and then down through the floor. Would this provide enough venting?
Finally there is a drain point on the bottom of the tank, my plan would be to run this through a 12v motorised valve with a switch mounted in the cab so that when at a drive over drain it would just be a case of flicking a switch when positioned correctly. I have ordered a 1/2" motorised valve but I'm beginning to think this might be too narrow. Is it likely to get clogged by sediment in the tank or does this tend to get broken down by driving?

Any advice would be greatly appreciated.

Thanks, unfortunately I don't think I have the space for a proper u bend. The outlet from the sink is only 25mm and has the connection for the corrugated hose. The fridge is just below this and the pipe only just clears the top of it. The route to the tank is very tight so conventional pipework won't work. My plan was once I had the pipe in the garage area under the fixed bed I would form a u bend with it. I could possibly use two 90 degree pipe connectors to do this so that the U is removable. Would this work or would it just be unnecessary restrictions in the pipe?

Our freshwater tank is mounted underneath the van in this area. Plus it would need to then come back into the van to get to the waste tank.

The threaded outlet at the bottom of the tank is a 1/2" outlet. Would it make sense to increase the diameter of the pipe to 1" out of this if it is already restricted at the outlet?

I have the valve on it's way from China anyway so might give it a go with the fitting that is there. I can always drill a bigger hole if it doesn't work.

My biggest concern is the venting, how big does the vent need to be and is it ok to run it out of top of the tank and then down through the floor. I had read that the vent should go to the roof but I'm not sure about this as there would be no overflow. Are there specific vents for this or is a pipe connection sufficient?

Great thanks for that I actually have one of those fittings that came with the tank, I thought it would be too small. Also have the hose from a condensing dryer that fits it so can use that.