Whether or not they remove the fill line, depends on how the tank is decommissioned. There are three ways an abandoned tank can be handled, as explained in this PDF
The 1997 Uniform Fire Code, adapted by WAC 51- 44, requires that
heating oil tanks out of service for a period of one year shall be
decommissioned by using one of the following processes.
- Removal from the ground and restoration of the site in an approved manner.
- Abandonment in place by filling the tank completely with an approved, inert solid material.
- Tanks of 1,100 gallons or less may be left empty provided they are first pumped and cleaned, and have the fill line capped or plugged,
below grade, to prevent refilling of the tank. (NOTE: Some local
juisdictions do not permit this “clean and cap” method. Check local
requirements before beginning any decommissioning process.)
In the first method, the tank is completely removed, so the fill line will also be removed. With the second method, the fill line may be left behind. In the third case, the fill line should be cut below grade before it's capped. So the fill line will still be there, but it will be at or below the level of the ground.
The document also has a good list of questions to ask the contractor.
Some important questions to ask contractors:
• Are they experienced?
Can they provide the names and telephone numbers of current or
recent customers as references?
• Do they have environmental
pollution liability coverage?
• Do they collect soil samples?
• Which laboratory do they use for the analyses?
• Where will the tank, oil, and contaminated
water from rinsing out the tank be disposed? Is
that disposal site insured?
• What documentation, labeling, and other
paperwork are provided? You should receive
documentation of disposal of the tank, a copy
of the lab results, documentation that the soil
samples were handled properly, a copy of any
permits required, and documentation of the
disposal and/or treatment of any wastes.
Call suburban, tell them that you don't want the tanks any more.
Make sure you are present when they unhook so there is no damage to your connection.
I recommend that you use a pair of tanks, so that there is always a spare on hand. One is disconnected and capped. (Bugs love to nest in the opening...)
Note that for emergency heating you can go through a tank of propane in a hurry. There may be merit in buying your own 100 lb tank, and parking it next to your hookup. You need a friend to horse it there, but it may be there for a LONG time before you need to refill it.
Also: Here in Alberta, you can get an older tank recertified (Pressure test and a new valve) for much less than the new cost. Not worth it for the barbecue size but for 40's and up it may be worth it. Many propane dealers are set up to do this.
A final thought: While $5 a gallon is too much, your project is going to save you only a hundred bucks a year, and the first year of that is gone to get your tanks. Is it worth it?
Keep your tanks painted to stop rust. Either aluminum or white.
Best Answer
First answer is that yes they will probably level out.
But whether this recurs depends on the source of the sludge. Simply blowing out the lines once probably will not solve the original problem.
If you can figure out the source of the sludge there may be remedies like settlement filters (like used on swimming pools).
You might also consider a larger size tubing.
Without more information it is difficult to give you a precise answer.
Good luck!