NO BLANKET RULE FOR WASHING BAGS
I have found that the answer to the questions of to wash or not to wash and how to go about it is different for just about every bag.
If a bag is in excellent condition, it is not stained, reeking of mildew or dander from the original Lassie, then, BY ALL MEANS keep it away from the laundry room.
After you have emptied it in the usual manner, disassemble the bag as carefully and completely as you can.
Take it OUTSIDE and wear a dust mask if you are particularly sensitive to such things. Turn the bag inside-out and shake/scrape/beat/brush/vacuum it until MOST of the dirt is gone.
I would then take the bag back inside to a well lit work area and complete clean all of the hidden pleats and seams with a vacuum and a small brush.
Then temporarily turn the bag right side out to carefully vacuum it clean as well. Again turn the bag inside-out and evenly and completely dampen BUT DO NOT SOAK it with a DISINFECTING and deodorizing product like LYSOL spray.
Allow it to completely air dry.
Turn it right side out again.
Inspect for holes and weak seams. Repair any by darning with matching thread AND/OR applying matching iron-on, cut-to-size fabric pieces on the reverse side.
Keep irons AWAY from screen printing! Protect it with a pressing cloth or iron that area GENTLY from the reverse side.
I have found that on Hoover & Kirby bags that one of the first things to cause trouble are the metal bag bands (Hoover) and the metal mounting springs (Kirby). They RUST, stain the fabric with same and if they don't completely fall apart, the abrasive rust particles they shed steadily grind away at the integrity of the surrounding fabric.
Rarely have I been able to successfully "slide" a rusted Hoover bag band out of its fabric sleeve without shredding the fabric and Kirby springs are completely enclosed. The remedy requires just a little bit more skill and practice than darning holes. A seam ripper or a pair of small manacure-like sewing siscors is needed to patiently and carefully open up the sleeve holding the band or the spring. Do this with an old towel in your lap to catch the shower of dirt and rust that will fall out of the sleeve.
Brush and/or vacuum the opened sleeve area as clean as possible. I have had little luck removing rust stains from these fabrics. I have even tried things like Lime-Away acidic cleaners. There MAY have been some improvement but maybe I was just trying to convince myself it was worth the effort and the acid could not have done the fabric any favors. The consolation is that more often than not these stains are almost completely hidden when the bag is reassembled and installed.
Hoover bag bands can be wire brushed and/or sanded smooth and reused, or, if necessary replaced with a NOS band or at least one in better condition. I've never tried, but I wonder if one of those self-tightening plastic cinch straps would be a good substitute?
Why Kirby used metal springs on their bags mouths remains a mystery to me. Nine times out of ten I find them crumbling with rust and broken into six pieces. I replace them with a standard-issue Eureka/Sanitaire conventional upright round rubber belt.
For Hoover bags, resew the sleeve either with the band in position or leaving enough room to slide it in later. Follow the original stitching holes as a guide. The first option requires three hands, the second, the patience of Job. You pick.
The belt or spring for Kirby bags must be sewn into the sleeve. Again, follow the old stitching.
If a bag is truly a diamond in the rough, is filthy dirty but is in otherwise good condition or shows promise of being repaired, by all means wash it! It is my understanding that most "modern" shake-out bags (read post 1925!!) depend on the tight weave of the fabric rather then chemical sizing for their filtering properties. Besides, if the choice is a beautiful, fresh bag or some nasty thing you don't even want to bring into the house, the choice is easy. The only bag that I have washed and then from which noticed across-the-room-visible dust leakage was from a Kirby Classic ?, constructed out of a denim-like material with vinyl pin stripes. . .decidedly cheaper and less effective than its predecessors.
I wash by hand or in a front loading machine on "hand wash" cycle with the bag turned inside-out, THOROUGHLY vacuumed and brushed and ALL hardware removed. If you have a top loading machine, use the most gentle cycle and only allow the machine to agitate very briefly two or three times over a half-hour soak.
Dark colors WILL bleed like CRAZY. So wash each bag separately.
Screen printing on Hoover bags WILL fade no matter how you wash them and, TRAGICALLY, can wash away almost completely if put in a machine.
I have had much better luck with Kirby screen printing.
Rinse repeatedly and gently until the water is as clear as it will be.
Add fabric softener to the last rinse.
Do NOT tumble dry. Do not wring if you hand washed the bag. Drip and hang dry, iron, protecting the screen printing, and proceed with reassembly and repair.
IN THEORY dry cleaning may be the best solution of all. Screen printing that dissolves in water just might come out completely unscathed from a bath in dry cleaning fluid. Similarly bleeding and fading may be less of an issue. I've just never tried it . . . .Hmmmmm.
I do go on!
Marty Kaplan