Something else to consider is lead possibly being in the marbles. Some have it, some don't. I wouldn't want lead aging in my wine. Google it.
It is always good to make a bit more must than what your final volume goal is. If you're shooting for a gallon, then make 1.25 gallons of must up. When you transfer from primary to secondary you will leave the gross lees behind and your total volume will decrease. By starting with an "overage" you have some extra mead to "top off" with. And, if you have extra after topping off, then put it in a pint, half-pint, quart, beer, whatever bottle with an airlock for future topping off. If you're making traditional mead then you want need as much extra. But, if you're making a melomel or something else with fruit in it then you will probably have an abundance of gross lees to remove...thus reducing the volume of remaining mead even more.
Transferring from primary to secondary can cause a great deal of loss when trying to dodge the lees. I've about decided that the best route is to stick the racking cane in one spot, let it vacuum up the lees surrounding that one spot until clean and then let it pull the rest of the mead out of the jug from that cleared area. You *will* get lees sucked up in the transfer so why not save some time and clear a spot to siphon from. The one thing you *don't want* is to be wiggling your racking cane around in the jug as you siphon..that can cloud up the entire jug.
When you've siphoned all that you can while avoiding moving the cane around...stop. The lees/sludge/whatever in the bottom of the jug can be poured off into a quart jar or a wine bottle if no large pieces of debris are present. Place the jar in the refrigerator for a week or two and cold crash it. The sediment/lees should settle to the bottom and leave clear mead on top. Carefully pour the clear layer into a smaller container of some type or add it to whatever you've already saved if there is room.
Since you will be holding this "overage" for a short while as you rack from time to time I personally thinking saving them in PET bottles is good. Plastic Gatorade bottles are good for this. The caps can easily be drilled, a grommet inserted, and an airlock installed...multiple sizes, too.