Update: Uploading a screw valve. This one you feed 4mm tubing through the entire way to the bottom of the tank. This keeps everything absolutely contained no matter your print method. The screw merely compresses the tube to control the flow. There is room for up to 10mm OD tubing to "buffer" the difference between the size of the valve and the 4mm tubing inside the valve. Fusion 360 was giving me trouble so please clean up threads after printing.

Update: This one is close to the finish line. Video demonstrating one of the more current versions live while printing. XL version to come, Im guessing about 100ml is the capacity of the current version. Dont feel like calculating volume. Maybe someone who knows there way around some CAD programs could figure that out. Im just making sure it works great, then looks good.

Version 2 files up now. Fixed missing channel in the upper reservoir channel. Slimmer top file. And after fussing with the Fusion, managed to work in a Tesla Venturi valve for syphoning the resin through safely. Pop in a 4mm tube in the available hole and "suck" the resin through. You may be able to "blow" the resin through, but I haven't tested how much vacuum pressure this can achieve in this configuration.

Uploading a second version of the Vat adaptor to suit the slimmer Vat on the LD-002H versus the LD-002R. To prevent confusion, they are appropriately named and old file removed. Removing damaged Valve Body file and uploaded full version. (I blame Fusion Boundary Fill). Oh and adding a simple Venturi siphon on the bottom of the valve. Install tube with 3mm ID, open valve and BLOW through the tube. I designed this in so no one will get resin poisoning when trying to syphon the resin through. Please use as intended. There are a few upward pathways to prevent fluid from traveling through the access port. You can cap it off if needed. Ill be redesigning the syphon access port for absolute one way travel of fluids in the future.

Uploaded a slimmer more pleasing to the eye upper res channel. Same purpose, just a little more cleaner.

Believe the Vat adaptor I made is just a bit too big to allow the print head to clear it. Ive made another one that's smaller and doesn't invade the print space. Designed to let the resin drip into the tray on the side of the Vat. Still 4mm tubing. Dont believe anyone can print faster than this can supply. If you end up needing more flow, let me know and Ill custom work the flow for you.
Ive uploaded a secured version of the reservoir and top. 2 x M3 12mm screws to secure those.

A very prototype resin fluid backup reservoir. I have not measured the volume capacity of the reservoir so I cant tell you how much this will provide until I do. Somewhere between 100ml and 200ml is what I guess. I liked the design this is inspired off of, but I wanted more accurate control over flow rate thus introduced a printable ball valve.

I'm not sure when this will become useful(It does, just the reservoir for this one took almost an entire Vat capacity printing 100% solid.). I have plans to take advantage of the flow rate to mix colors at a steady rate and/or layer the colors in the reservoir so they change slowly over-time without human intervention.

References used:
https://www.thingiverse.com/thing:4485628
https://www.thingiverse.com/thing:3371302
Inspired by:
https://www.thingiverse.com/thing:3777796
Video Demonstration:
https://youtu.be/GW-9Xb1-vCE