Hi there,
unfortunately benadryl is a diuretic which pretty much guarantees you will have to pee constantly when you ingest more than allergy doses. It can be dangerous having to walk yourself to the bathroom on a hefty dose of benadryl, I would have a pee bucket set up, like a good 3 gallon or something, depending on your dosage you might fill up the 2 liter bottle pretty quick and end up with a urine soaked bedroom floor. At 700mg+ the amount of piss that comes out of you is astronomical, i've made the mistake of only having a single pop bottle at the ready to have it overflow in two pees, luckily not onto carpet. Benadryl just sucks every last morsel of moisture out of your body so whenever you piss it's like you have been holding it in for hours and hours when really you just took a piss 5 minutes prior.
Have the bucket placed close to wherever you will be laying down so you don't have to fumble around and fall into a wall or something when you have to urinate(falling into walls is a very real danger on benadryl, it fucks with your gravity center I guess, walking is very dangerous if you lose concentration for even a split second).
I haven't done benadryl in deliriant-tier doses in years, I have no idea what I liked so much about those crazy ass trips back in the day. It has a nice anti-depressant+stimulant feel to it at medium doses though that got me through a lot of bad times in my life when I don't think I could have taken all the emotional b.s. that would have raped my mental well-being, I was glad to have benadryl around all the time to numb myself a bit. I'm going through some b.s. right now actually and might have to think about getting back to my old regimen of taking medium doses just to numb myself a bit, weed is just making me think of the same shit more intensely, I don't want to get back into hard drugs as adding some serious withdrawals into the mix will make aiming a projectile into my cranium seem like cake. A psychedelic wouldn't do shit for me in this state either, it's not even worth a second thought, the last trip I took had me hearing the waling horn of satan's truck screaming into the night like he was on the search for lost souls to abduct when I was on the downturn...I feel like I got possessed by evil spirits or something, even though the night started off good it all went south towards the end.