If you use a wooden stick as your measuring device you can carve the marking in and then you don’t have to worry about the marker. I use a yard stick and measure from the surface of the wort to the top lip of the pot so it never actually comes in contact with the wort, or barely. That works to.
Keep the kettle. You might start reducing first running a. You might start doing decoct ions, or cereal mashes. You might do a big batch and want to split the boil. You could use it as a grant if it has a valve.
Do not ask how many pots and kettles I have in the garage!
A pic will do. 
This is how I usually manage my boils. I have a 7.5 gallon turkey fryer, and do 5-gallon all grain batches.
I run off about 6.5-7 gallons into the fryer, and run an extra 1-2 gallons into a 5-gallon brewpot that I got with my original kit. (I boil off about 1.5 gal/hr). While the boil is going, the extra wort is kept at a boil (or close) on my kitchen stove. Once I get down to about 5.5-6 gallons in the kettle (usually about 45 minutes in), I pause my timer, add the rest of the (near) boiling wort to the kettle, and then restart the timer once the wort gets back to a boil. My tongue has not noticed any hop utilization problems.
The first thing I would do is buy an adjustable propane regulator Shop by Category | eBay . You are wasting a lot of money if not turning your flame down after boil starts And for a larger kettle I bought mine from Sams.com. It is aluminum and works just fine and is lighter and a lot Cheaper than stainless. http://www.samsclub.com/sams/the-backyard-classic-pro-outdoor-stock-pot-100-qt/prod2540475.ip
Why are so many people stuck on 5 gal batches. Does not cost that much more to step up to 15 gal and basically takes the same amount of time. Still do 5gal for Barley Wines and Stouts and Tripples
That’s a damn good price on the kettle.
I’ve got a 10 gallon pot that loses about 2.25 gal per hour to evaporation. Preboil is about 7.5 gal (which I measure with an oak dowel that I marked with Sharpie…works every time)…I use Fermcap-S to control the hot break and foaming. I also back the flame off so it doesn’t foam as much while it’s boiling. I’d love to have a 15-20 gallon Blichmann kettle and burner, but I make great beer with what I’ve got. We as brewers have to adapt to our equipment, somewhat. BTW, I think you’re going to find that evaporation rates of well over 20% are fairly common.
+1 to making the most of what you have. I have the same size pot and brew similarly , including the wooden dowel which helps with volume accuracy. I’d love a Blichman but I doubt I’ll ever bother.
The first thing I would do is buy an adjustable propane regulator
Got one. The experience I’ve had with my setup is that there’s a very fine line between boiling and not. If I leave the flame too low the boil will occasionally just stop. If it’s in the mood it will start again without intervention. I suspect it has more to do with the burner, which has no wind shield on it.
It is aluminum and works just fine and is lighter and a lot Cheaper than stainless.
I started with an 8-gallon aluminum kettle. Nice jobby that I bought at a restaurant supply store for a decent price. It’s now nicely pitted inside because I left it filled with PBW for far too long.
Stainless is more expensive but it has advantages. My current kettle is lighter than that old aluminum one because it is much thinner. And you almost never see welded ports on aluminum.
Why are so many people stuck on 5 gal batches. Does not cost that much more to step up to 15 gal and basically takes the same amount of time.
For me it’s because I don’t drink my homebrew very quickly. Let’s do the math: 1 beer drinker in my house x 1 pint per day (on average) x 90 pints in a 5-gallon batch = about 3 months to drink a batch IF that’s the only beer I drink. Which I don’t. Got 3 kegs running and a cellar full of bottles, both mine and from the store.
Eventually I get tired of my kegs being occupied so I take them to the office to have them drained. Point being that the reason I don’t make more beer is because I simply don’t need that much beer.
We as brewers have to adapt to our equipment, somewhat
I don’t disagree. It’s not a universal equation, though. If you have the capability to improve your equipment, either the money to buy it or the expertise to build it yourself, don’t you?
I admit to having both perfectionist and gadget-freak shades to my personality. Frustrations like my boil kettle tend to become opportunities to play with new toys.
BTW, after doing some research on kettles, I find that Blichmann actually comes out OK for value. When you add up all the cost of all the bells and whistles, there aren’t many feature-equivalent off-the-shelf solutions at a better price. Been talking with my LHBS, though. They do welding and might be able to put a deal together for me.
Still searching for my perfect kettle…
Blichman may (may) have a resale bump too. Kind of the Harley of homebrew equipment (kind of)
God, I wish my 5 gallon batches had 90 pints in them…mine only have about 40. :o
+1 !
Hey, he’s just ahead of the curve. He’s talking about the new pints that brewers and sellers will be offering- much like the four-packs that the craft brewers are so proud of…
Yep, I fudged up that math quite well. Why is there no facepalm emoticon?
In any case, point being that I simply don’t go through my kegs very quickly, at least not without help.
you need help going through your kegs!!! Well, why didn’t you say so…I’d be happy to help. ;D