I would not recommened a Submersible pump.
I had one when I started wfp, I checked its condition on a regualer basis. If you usea gavalnized jubille clip,the clip will start to rust within 6 weeks.
I then used a stainless steel jubille clip which would rust within 6 months.
After a year of my sub pump living in my IBC tank I decided to pull it out and check it over as when I went away on holiday the tds of the water would start to climb, So I know something was contaminating the water.
On taking the sub pump apart, I find out that though the outside was all plastic the impeller and many oher parts you cannot see were made of metal which was rusting like mad. The pump worked fine but it was contaminating my pure water.
I then bought an external Transfer pump that sits on top of my IBC tank, A 1" hose is attached to the pump and I pushed this hose through some plastic pipe so the pump sucks the water up from the very bottom of the tank and keeps the hose straight in the tank. If you dont use a plastic pipe to push the hose through the hose floats around in the tank.
I now never worry about the sub pump rusting. Its a lot better. I will try to post a pic this weekend.
Neil