Major water leak coming out underneath trailers black cover

Thank you everyone. Great suggestions and we can look Friday and let you know what we see. I did look at the manuals but unfortunately it doesn't give me enough info. We did locate another handle under the slider by tires black handle. Manual doesn't say what it is. I was afraid to pull it as I thought it is a manual lever to disengage the auto slider. Old biscuit I think this is what your referring to. I'm going to pull it. One question should it stay open? Thanks you.